In the field of electronics, a linear regulator, or linear voltage regulator (LVR), is a system used to maintain a steady voltage at a node, such as an output node for supplying a load. Two general configurations of linear regulators include a series regulator, where the regulating device is located in series with the regulated load, and a shunt regulator, where the regulating device is located in parallel with the regulated load. A simple example of a linear regulator includes only a Zener diode and a series resistor. More complicated examples of linear regulators include separate stages for implementing voltage reference, error amplification, and power pass elements.
In a slightly more detailed example, a transistor is used in a linear regulator to establish the regulated output voltage. The output voltage is compared to a reference voltage to produce a control signal for the transistor which adjusts the current supplied through the transistor. Such linear regulators do not require magnetic devices such as inductors or transformers, which can be relatively expensive or bulky. Basic components used in many linear regulators include transistors, diodes, and resistors, which are readily fabricated using microfabrication techniques for integrated circuits.
Because linear regulators generally operate using a variable voltage drop to regulate voltage at an output node, the supply voltage provided to an input of the linear regulator is generally required to be at least some minimum amount higher than the desired output voltage at the regulated output node. This minimum voltage above the desired or target output voltage is often referred to as the dropout voltage. Thus, the minimum supply voltage is equal to the target regulated output voltage plus the dropout voltage. For example, linear voltage regulators with low dropout voltages are often referred to as low dropout regulators (LDOs).
Thus, many types of linear voltage regulators exist for providing regulated supply voltages in the presence of varying load conditions. These linear regulators may be implemented in an on-chip manner; however, due to stability and transient response requirements of the on-chip environment, an off-chip capacitor is often implemented as part of the voltage regulator. An off-chip capacitor increases manufacturing costs and space usage, and also prevents a fully on-chip implementation of a system. Off-chip capacitors often have capacitance values in the range of 500 nanofarad (nF) to 10 microfarad (μF) or higher.